Thin film transistor substrates are provided with, for example, thin film transistors (hereinafter also referred to as TFT) as switching elements for respective pixels which are the minimum units of images.
Passivation films, which are insulating films for protecting TFTs, lines, etc., are formed on substrates to improve the reliability of thin film transistor substrates. The passivation films are inorganic insulating films such as silicon oxide films and silicon nitride films.
Thin film transistor substrates generally include gate electrodes, source electrodes, and drain electrodes forming the above-described TFTs and lines. These electrodes and lines are made of copper (Cu) having low resistance and requiring low costs.
However, copper is generally less adhesive to glass substrates and insulating films such as the above-described passivation films, and thus electrodes and lines made of copper are easily removed from the glass substrates and the insulating films.
In order to address the problem, a thin film transistor substrate is disclosed, which includes electrodes and lines made of a copper alloy containing at least one selected from the group consisting of titanium (Ti), aluminum (Al), and magnesium (Mg) at a concentration ranging from 0.1 to 10 at %.
For example, conventional art teaches as follows (see, e.g., Patent Document 1). When a source electrode, etc., made of a copper alloy containing titanium is fabricated, a film of the copper alloy is formed and then subjected to thermal treatment (e.g., at 350-450° C. for 30-120 minutes). Titanium is then diffused to the surface of the film and reacts with oxygen of air to form a titanium oxide (TiOx) film on the surface of the copper alloy. As a result, the adhesiveness with a glass substrate and an insulating film such as a passivation film improves.